By setting a role precondition, SELECT_NAVIGATIONAL and the RESTful
Web service will not display a link to the other end of the association
for the rows that do not match the Role precondition.

You only can define a Role precondition on an end point when the other
end point has a multiplicity of * or 0..1. This means that at the other
side of the end point there may not be an element that matches the
Condition mapping.

Example:

Let us say that we have an association between the views employee
and supportcase and we know that only the employees of the
department 50 (support) have support cases assigned to them.

When querying the view employee with SELECT_NAVIGATIONAL or the
RESTful Web service, the output will include the links of the
association for each row. However, only the links of employees of the
department 50 will have support cases associated to them.

Therefore, we can set a role precondition DEPT_NO=50 in the end
point of the view employee.

By doing this, when the user queries the view employee,
SELECT_NAVIGATIONAL or the RESTful Web service will not display the
link of the association for the employees that do not belong to the
department 50.